Powder for high strength dust core, high strength dust core and method for making same

Abstract

A mixed powder useful as a starting material for dust core comprises a uniform mixture of a soft magnetic powder and a binder resin so that the resultant dust core has an electric resistance capable of suppressing an eddy current between the soft magnetic powdery particles and high mechanical strength at room temperatures and also at high temperatures. In the mixed powder, the binder resin is made of a phenolic resin powder which has a methylol groups in the molecule and preferably has an average particle size of 30 μm or below and wherein when the phenolic resin powder is dissolved in boiling methanol in large excess, a content of an undissolved matter is at least 4 wt % based on the total of the phenolic resin. A dust core obtained from the mixed powder and its fabrication method are also described.

What is claimed is:  
     
       1. A powder for high strength dust core comprises a soft magnetic powder and a powder of a phenolic resin powder wherein when said phenolic resin is dissolved in boiling methanol at a rate of 1 g of said phenolic resin per 100 ml of the boiling methanol, a content of an undissolved matter is at least 4 wt % based on the total of said phenolic resin. 
     
     
       2. A powder for high strength dust core according to  claim 1 , wherein the phenolic resin powder has an average particle size of 30 μm or below. 
     
     
       3. A powder for high strength dust core according to  claim 1 , wherein said phenolic resin powder is contained in an amount of 0.5 to 5 wt %. 
     
     
       4. A powder for high strength dust core according to  claim 1 , further comprising a lubricant in an amount of at least 0.2 wt %. 
     
     
       5. A powder for high strength dust core according to  claim 1 , wherein a lubricant is contained in an amount of 0.2 wt % or below, inclusive of 0 wt %, and said powder for high strength dust core is used for a compacting process which makes use of a die whose inner wall surfaces are applied with a lubricant thereon. 
     
     
       6. A dust core characterized in that said dust core is obtained by curing a phenolic resin present in a green compaction of a powder for high strength dust cure recited in  claim 1 . 
     
     
       7. A method for making a high strength dust core, characterized by comprising the steps of compacting a powder for high strength dust core recited in  claim 1 , and curing a phenolic resin present in the resulting green compaction.